Antenna system

ABSTRACT

An antenna system including a support structure and an antenna assembly having an open grid reflector structure in a closed ring and dipole elements. The antenna assembly includes a number of antenna panels, each including a number of the dipole elements, the closed ring is self-supporting and connected to the support structure by radial beams and struts, and the antenna panels are interconnected by a variable angle connection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel antenna system having increasedcapacity, easy assembly, fewer parts, high strength and the capabilityof enduring high wind-loads and low temperatures. This is accomplishedby an antenna system comprising a closed ring of antenna panelssupporting multiple lobes. The antenna system has a modular structurewith exchangeable parts for economical transportation and manufacturing.The antenna system is easily adaptable to various conditions. Thestructural parts have an aerodynamic design and possible de-icing meansfor enduring severe climatic conditions.

The invention is related to the following patent applications with thesame filing date as the present application or to be filed in the nearfuture, having the same owner as the present application and entitled:

METHOD AND ARRANGEMENT OF CONVERTING A CELLULAR TELECOMMUNICATIONSYSTEM;

ROTATING LOBE ACCESS METHOD;

SELF-SUPPORTING RADIO BASE STATION;

2. Discussion of the Background

The technological status of the analog cellular mobile telephonystandard of today has a history going back to the late 70-ies. Thepresent technology is a development of the systems from the early days.

The base stations are mostly omnidirectional sites (circular cells) ortrisector sites (3×1200 cells). At the time of design it was consideredto be enough with this cell structure. The antennas used areomnidirectional or 60° sectorized antennas with low antenna gainrequiring high power RF (Radio Frequency) transmitters in both the basestation and in the mobile unit.

Existing cellular sites typically have 3 sides and each side has tworeceiving and two transmitting antennas spread out at a width oftypically 3-6 meters, but each antenna and cell radio is only getting aneffective use of 0.3×2.5 m with a width/height (W/H) ratio of 0.10-0.25.Thus only three different lobes and cells cover the horizon.

For a high capacity cellular antenna system it is much more importantthat the antenna has a wide diameter (=width) than it has height.Traditional cellular antennas typically are 0.3 m wide and 2.5-3.5 mhigh at 800/900 MHz or 0.7 m wide at 450 MHz and supports one 60° lobeand a 120° wide cell.

Thus, the prior art antenna systems typically have is high powerconsumption, high back lobes and high interference levels due to thereasons stated above.

SUMMARY OF THE INVENTION

The present invention proposes an antenna system having a ring antennamodular principle consisting of coupled grid panel reflector antennashaving low back lobes, very high gain and capacity and low wind drag.

The invention and further developments of the invention are set out indetail in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an overall view of a mast provided with a phased array antennain accordance with the invention;

FIG. 2 is a cutaway view of a panel of the antenna and its mountingarrangement to the mast;

FIG. 3 is a perspective view of a panel of the phased array antenna inaccordance with the invention;

FIG. 4 is a cutaway front view of a corner of the panel of FIG. 3

FIG. 5 is a cutaway rear view of a corner of the panel of FIG. 3;

FIG. 6 is a perspective view of a dipole element mounted on atransformer beam of the invention;

FIG. 7 is a view in longitudinal cross section of a dipole and atransformer beam of the invention;

FIG. 8 is a detail view of the lower connection between two panels;

FIG. 9 is a detail view of the lower connection between two panelssimilar to FIG. 8 but without the horizontal strut; and

FIG. 10 is a cross-sectional view of the oval horizontal strut.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, and moreparticularly to FIGS. 1-10 thereof, there are illustrated embodiments ofthe present invention, as will now be described.

The present inventors have realized that the available frequencyspectrum may be used more efficiently through installation of phasedarray antennas. The phased array antennas will enable the use ofmultiple lobes (from 8 to 100 or more per site). Each lobe can betreated as a cell which will make it possible to more effectively reusethe available frequency channels. The capacity can be further increasedif the higher antenna gain in the phased array antennas is used to allowfor a decrease of transmitted RF cower from both the mobile terminalsand the base with a factor of 2-40 depending on antenna gain andsectorisation in the system.

The antenna system is modular and can be configured by:Number of panels1-20 for maximum gain and directionality. Mast or building mountedreflector variants with different environmental backlobe and wind loads.Vertical height and gain variations 2-4-(6) dipoles. Different dipolerow variants for: frequency, bandwidth (BW), lobe tilt, null fill up,connector location, wind area.

All variants have the same fixing holes and location and are thusselectable at installation or modifiable after installation if thenetwork structure or traffic demand changes considerably. Also onedipole row can be removed for repair or upgrading without interruptingthe operation, causing only minor performance loss.

Existing masts/towers are surveyed in order to collect structural dataand locate available space for the new antennas. The collected data isused for planning of the antenna installation at each site.

After one of the reflector types and maximum possible quantity of panelshave been determined and selected to suit the available tower strengthand desired traffic, the best suitable dipole rows are selected. It mayturn out that in different directions, the requirements vary withdifferent capacity or range or beam tilts and different reflectors areoptimum and possible. Dipole row variants can be selected and installedseparately.

In the new antenna system each radio has coherent signal access toalmost the full width of all antenna panels pointing to the actualsubscriber. W=2.5-15 m and H=2.5-1.25 m gives a W/H ratio of 1.0-12.

In FIGS. 1 and 2 a mast fitted with the antenna system of the presentinvention is shown. A mast may be an old mast having an old antennasystem (not shown) and the present antenna system may be installedwithout interrupting the traffic of the old antenna. As may be seen fromFIG. 1, the antenna system 1 comprises a closed outer ring 2 of panels 5or sections. This outer ring 2 of panels 5 is connected to an inner ring3 by horizontal beams or struts 4. The inner ring 3 is in turn connectedto the mast 6.

FIG. 2 is a cutaway view with only one panel shown for better clarity.With reference also to FIG. 3, the panel consists of horizontal beams 7,vertical grid rods 8 and vertical transformer beams 9 on which dipoleelements 10 are mounted. The panels are interconnected by upper andlower connections which are described more in detail below. Thehorizontal supporting struts 4 are connected to the inner ring 3 byupper and lower connections, which are also described more in detailbelow. Inside the inner ring a number of low wind area antenna boxes 11are fixed to a floor 12. The antenna boxes 11 contain duplex filters(DPX), low noise amplifiers, transmitter power amplifiers and combinersas well as lobe-shaping och distributing equipment. The design andstructure of the antenna boxes and the equipment associated therewith donot form any part of the present invention.

As an alternative, the antenna boxes may be located on the ground if themast is low.

The antenna is almost self supporting by its horizontal and verticalmembers leading to the four bolted corner joints and to its neighbour.

The panel ring can be supported vertically to the mast structure bydiagonal thin wires (not shown) having low wind area and weight, similarto a guyed sailboat mast. Diagonal struts (not shown) may also beprovide between the inner 3 and outer 2 rings.

The mast mounting supports a low loss close cable distance and mountingof the low wind area antenna boxes.

The same antenna aperture is used for both transmission and receptionvia DPX filters, one per dipole row, which will operate with very lowintermodulation products due to the reduced RF transmission powers. Thisis not practically possible in a traditional antenna installation with50 W transmitters and high sensitivities, at -116 dBm.

With the antenna panels coupled close to each other in a continuousring, the following is obtained at the same time. Back lobes are reducedby the eliminated lateral end effect. Back lobes originating through thegridded reflector or around the upper and lower edges meet a continuoussecond wall reflector giving additional attenuation in the reversehorizontal angles.

A continuous connected self-supporting wheel ring structure requiringfew additional wind area and low weight mast mounting rods. These rodsare essentially radial and horizontal and are elliptically shaped tohave a low Cd, against horizontal winds from all azimuths. The strongring structure is ideal to support an antenna system with a high antennaaperture W/H factor of 1-20.

Amplitude and phase tapering is used on most radio channels and on 1/3or 1/4 of all horizontal vertically mounted dipole row inputs. In thisway a very narrow horizontal lobe with the width of appr. 60°×lambda/W,and with low side lobes and back lobes can be pointed to each user,significantly increasing capacity and link budget and power efficiency.

In FIG. 3 is shown a sector of a phased array antenna to be installed inaccordance with the present invention.

The radio tower or mast is complemented with phased array antennasinstalled together with the existing antennas in order to permitcontinuous operation of the analog system during the installation of newhardware.

The phased array antenna comprises at least one sector, such as shown inFIG. 3. It is built up on an aluminium framework where 32 dipole antennaelements 10 are arranged in eight vertical rows, each row containingfour dipoles 10. At each side of the rows are aluminium rods 8 placed.The aluminium rods 8 are acting as reflectors.

The reflector panel 5 comprises oval horizontal beams and round verticalrods welded together in each crossing. The panel has a joint in thecentre so that it may be lacquered and transported in two halves.

As is shown in FIGS. 4 and 5 the transformer beams 9 on which the dipoleelements are welded are fastened with screws to brackets 13 to thehorizontal beams 7 of the panels. Thus, it is easy to replace one dipolerow for repair or service.

In FIG. 6 the transformer beam-9 is seen from the end. The transformerbeam has three sections in which brass rods (not shown) are inserted andfixed with plastic distance elements forming three coaxial conductorswith the transformer beam as outer casing. The arrangement may also beseen from FIG. 7, in which the sectors are shown with phantom lines.

FIGS. 8 and 9 illustrate how two panels are interconnected at a lowercorner. The top and bottom horizontal beams 7 of two panels areoverlapping and secured together by a bolt through holes at the end. Aconnector plate 14 has a hole pattern for bolting the bottom horizontalbeams together at a fixed angle. Various connector plates havingdifferent hole patterns are provided for different versions of theantenna system having different numbers of panels and, consequently,different angles at the connection. A horizontal strut 4 is also boltedto the connector plate 14. In FIG. 9 the horizontal strut is not shownfor better clarity.

In FIG. 10 a transverse cross-section of the horizontal strut 4 isshown. At each side, the horizontal strut has a compartment foraccomodating a number of cables 15 for feeding the signals to therespective transformer beams. In FIG. 10 four cables 15 are shown ateach side. The compartments are covered by a cover 16 fastened withscrews to the horizontal beam. The cover 16 may be removed easily foraccess to the departments for inserting the cables and inspection etc.

Each dipole row are fed in parallel from the lobe shaping unit. The lobeshaping unit is in its simplest form a Butler matrix or similar phaseshifting equipment. The lobe shaping unit is shifting the phase of eachindividual input to the antenna inputs. The phase-shifted signals willwhen applied to all eight inputs radiate in a combined pattern at anangle from the antenna plane with a main power variable distributionwidth of about 15°. Each antenna array or sector with eight dipole rows(inputs) can form eight independent lobes. Thus, using a 8 sectionantenna, 8×8=64 individually controllable lobes are obtained.

Reflector variants are available for the following:

1. Wind loading max. 43 m/s or 60 m/s depending on climatic location

2. Safety factors (SF) 1.1 or 1.3 for rural or populated areas

3. Rural or urban reflector gain versus capacity

4. Rain protection, i.e. plugs and covers

5. De-icing by electric wires or heating fans (not shown) in certaincountries and areas

The reflector is available in 4 strength variants and reflectordensities

    ______________________________________                                        60 m/s        SF    = 1.3     Urban capacity                                  60                  = 1.1     Rural range                                     43                  = 1.3     Urban capacity                                  43                  = 1.1     Rural range                                     ______________________________________                                    

The grid reflector is wideband with fo=450 MHz. Medium or low back lobeelectrical versions are available.

The reflector is split in two halves for easy transportation and boltedtogether.

The rural reflector higher gain variant (not shown) has three rodsbetween the dipole rows giving lowest wind loading supporting a gainincrease by more panels installable.

The urban reflector higher capacity variant, such as shown in FIG. 3,has four rods between the dipole rows having lower back lobes andtherefore higher capacity.

Vertical rods are circular .o slashed.8 or 5 mm having low wind drag andvisibility.

A semivisible urban variant with ▭6 or 5 mm solid rods with four rodsbetween dipoles and 50. tighter horizontal 5×25 mm bars.

The dipole rows are available in four bandwidth and frequency variantsat SWR<1.3

    ______________________________________                                        450-470 BIN  20 MHz   fo =   460   D = 12 mm                                  400-500     100 MHz          450   D = 25                                     380-480     100 MHz          430   D = 25                                     380-512     132 Mhz          446   D = 30                                     ______________________________________                                    

As an alternative, a rural dipole and transformer variant with 1.1 timeshigher vertical height and gain +0.4 dB at the expense of slightlyhigher back lobes is provided. This is in combination with only 30 dBfirst vertical zero fill up.

The dipole elements are available in thick or thin diameters .oslashed.25 or .o slashed.12 mm, respectively, for 100 or 20 MHzbandwidth.

The transformer beams are of diameter .o slashed.29 mm air insulated, or.o slashed.20 mm to reduce wind load and visibility, optionally withsleeved humidity insulator (not shown).

Dipoles of aluminium thickness 2-1.8 mm welded to the transformer in onepiece without screws for low weight and low nonlinearities as is shownin FIGS. 4 to 7.

Coaxial connectors (not shown) are provided at the bottom or top of thetransformer beams.

    ______________________________________                                        Vertical lobe tilt available                                                                        -2, -4, -6 degr.                                        Vertical first zero fill up                                                   available             -30, -25, -20                                                                            dB                                           and second zero       -35, -30, -25                                                                            dB                                           and first lower side lobe reduced to                                                                <-15, -18, -20                                                                           dB                                           and second lower side lobe reduced to                                                               <-18, -21, -23                                                                           dB                                           ______________________________________                                    

Also the dipole rows are transported separately and screwed together atsite.

Dipole row mounting principle:

1. Hang on,

2. Snap in,

3. Secure winged nuts!

Obtained by:

Winged nuts on nylon strap

Solid electrical contact surface

The elliptic mast to antenna connection beams 4 are available in fourdifferent strength sizes, covered by three different outer dimensions35×100, 50×175 and 70×200 mm that also can house 8 runs of 1/2" or 3/4"coaxial panel cables 15 reducing cable wind drag and exposure, as isshown in FIG. 10.

The use of a highly directive high gain antenna system will make itpossible to use low power transmitters in both up and down link (0,1 Wuplink and 20 W peak, 5 W average downlink) which together with aminimum 48 dB fast adaptive power control function in both the uplinkand the downlink will significantly improve the link budget and thepower balance in the system. This is an important feature which willkeep the co-channel interference under control and increase thepossibility for channel frequency reuse.

The scanning lobe principle, the low noise amplifiers, the combiner, thebase station controller principle and the lobe shaping unit aredescribed more in detail and separately claimed in the above-mentionedpatent applications.

New combiners are installed together with a lobe shaping unit and a newbase station controller. The combiners will interface existing radioequipment to the new antenna system. Between the antenna array and thecombiners a lobe shaping unit will be installed for phase control andlobe forming.

Up to 160 narrow fixed or individual lobes and cells can cover thehorizon. This can enable tighter frequency reuse and a capacity increasefrom 4-64 times, and a RF power reduction of from 4-100 times, both atthe base station and the mobile station. This is of very big economicaland convenience importance for the end users and the operator.

The open grid circular and elliptic reflector construction gives a windloading that is typically <25% of a traditional plate and radome dipoleantenna, or stripline type, enabling existing masts to be employed.

Another feature included in the design is by optimizing for small crosssection aluminium rods of 5 to 29 mm thickness, meaning that >75% of thefront area is fully open and transparent. With the rods painted verylight grey-white the antenna becomes semivisible or discreet atdistance.

Variations

Also a reflector with the same 4 strength and grid densities isavailable, but with a fixed welded size of H=1220 mm and W=2550 mm. Thissupports maximised capacity in cities but has 3 dB less gain and issuitable on building roofs. The dipole rows for this smaller antenna are2 dipoles high, but otherwise the same.

More range gain than capacity gain at 450 MHz can be obtained by:Parallel connected 2 rings vertically by 8 panels ring 1 and 8 panelsring 2. Vertical height=2.6×2=5.2 m. Vertical lobe=14/2=7 degreesDiameter 6.2-6.6 m. Circumference=8×2.6=20.8 m. Only 8 antenna boxes areneeded and lower in cost than 16 panels in 1 ring.

The same principles as the vertically polarised antenna above but alsowith only or both horizontal elliptical dipole rows and closer distanceof the elliptical reflector horizontal rods are possible.

This is to give a horizontal diversity polarisation output or input viaseparate duplex filters.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. An antenna system comprising.a supportstructure; and an antenna assembly having an open grid reflectorstructure in a closed ring and dipole elements, wherein the antennaassembly comprises a number of antenna panels, each comprising a numberof said dipole elements, the closed ring is self-supporting andconnected to the support structure by radial beams and struts, and theantenna panels are interconnected by a variable angle connection.
 2. Theantenna system according to claim 1, wherein each antenna panelcomprises a grid of vertical reflector rods, horizontal support beams,and vertical transformer beams on which the dipole elements are mounted.3. The antenna system according to claim 2, wherein the horizontalsupport beams are oval in cross section and the vertical rods andvertical beams are round in cross section.
 4. The antenna systemaccording to claim 3, wherein the vertical transformer beams arechanneled and include three sectors.
 5. The antenna system according toclaim 3, wherein electrical equipment is located on a platform insidethe support structure or at a lower level.
 6. The antenna systemaccording to claim 3, wherein the support structure is an existing radiomast.
 7. The antenna system according to claim 3, wherein the supportstructure is an existing building structure including one of a chimneyand a tower.
 8. The antenna system according to claim 3, wherein staysare fixed to the antenna panels.
 9. The antenna system according toclaim 2, wherein the vertical transformer beams are channeled andinclude three sectors.
 10. The antenna system according to claim 9,wherein electrical equipment is located on a platform inside the supportstructure or at a lower level.
 11. The antenna system according to claim9, wherein the support structure is an existing radio mast.
 12. Theantenna system according to claim 9, wherein the support structure is anexisting building structure including one of a chimney and a tower. 13.The antenna system according to claim 9, wherein stays are fixed to theantenna panels.
 14. The antenna system according to claim 2, wherein theclosed ring is connected to upper and lower inner rings of horizontalsupport beams, the inner rings being connected to the support structureby radial beams and struts.
 15. The antenna system according to claim 2,wherein the variable angle connection is a connection plate having ahole pattern for bolting two panels.
 16. The antenna system according toclaim 2, wherein electrical equipment is located on a platform insidethe support structure or at a lower level.
 17. The antenna systemaccording to claim 2, wherein the support structure is an existing radiomast.
 18. The antenna system according to claim 2, wherein the supportstructure is an existing building structure including one of a chimneyand a tower.
 19. The antenna system according to claim 2, wherein staysare fixed to the antenna panels.
 20. The antenna system according toclaim 1, wherein the closed ring is connected to upper and lower innerrings of horizontal support beams, the inner rings being connected tothe support structure by radial beams and struts.
 21. The antenna systemaccording to claim 20, wherein the variable angle connection is aconnection plate having a hole pattern for bolting two panels.
 22. Theantenna system according to claim 20, wherein each antenna panelcomprises a grid of vertical reflector rods, horizontal support beams,and vertical transformer beams on which the dipole elements are mounted,andthe horizontal support beams are oval in cross section and thevertical rods and vertical beams are round in cross section.
 23. Theantenna system according to claim 20, wherein each antenna panelcomprises a grid of vertical reflector rods, horizontal support beams,and vertical transformer beams on which the dipole elements are mounted,andthe vertical transformer beams are channeled and include threesectors.
 24. The antenna system according to claim 20, whereinelectrical equipment is located on a platform inside the supportstructure or at a lower level.
 25. The antenna system according to claim20, wherein the support structure is an existing radio mast.
 26. Theantenna system according to claim 20, wherein the support structure isan existing building structure including one of a chimney and a tower.27. The antenna system according to claim 20, wherein stays are fixed tothe antenna panels.
 28. The antenna system according to claim 1, whereinthe variable angle connection is a connection plate having a holepattern for bolting two panels.
 29. The antenna system according toclaim 28, wherein a antenna panel comprises a grid of vertical reflectorrods, horizontal support beams, and vertical transformer beams on whichthe dipole elements are mounted, andthe horizontal support beams areoval in cross section and the vertical rods and vertical beams are roundin cross section.
 30. The antenna system according to claim 28, whereineach antenna panel comprises a grid of vertical reflector rods,horizontal support beams, and vertical transformer beams on which thedipole element are mounted, andthe vertical transformer beams arechanneled and include three sectors.
 31. The antenna system according toclaim 28, wherein electrical equipment is located on a platform insidethe support structure or at a lower level.
 32. The antenna systemaccording to claim 28, wherein the support structure is an existingradio mast.
 33. The antenna system according to claim 28, wherein thesupport structure is an existing building structure including one of achimney and a tower.
 34. The antenna system according to claim 28,wherein stays are fixed to the antenna panels.
 35. The antenna systemaccording to claim 1, wherein electrical equipment is located on aplatform inside the support structure or at a lower level.
 36. Theantenna system according to claim 35, wherein the support structure isan existing radio mast.
 37. The antenna system according to claim 35,wherein the support structure is an existing building structureincluding one of a chimney and a tower.
 38. The antenna system accordingto claim 35, wherein stays are fixed to the antenna panels.
 39. Theantenna system according to claim 1, wherein the support structure is anexisting radio mast.
 40. The antenna system according to claim 39,wherein the support structure is an existing building structureincluding one of a chimney and a tower.
 41. The antenna system accordingto claim 39, wherein stays are fixed to the antenna panels.
 42. Theantenna system according to claim 1, wherein the support structure is anexisting building structure including one of a chimney and a tower. 43.The antenna system according to claim 42, wherein stays are fixed to theantenna panels.
 44. The antenna system according to claim 1, whereinstays are fixed to the antenna panels.